Many items of perishable produce respire after harvest. That is they consume oxygen and produce carbon dioxide. It is known that if the rate of respiration can be slowed during transportation, the produce will degrade less. The rate of respiration can be controlled by controlling the amount of oxygen and/or carbon dioxide available to the produce.
Many items of produce deteriorate after removal from the plant. This deterioration which is usually given the term senescence, can be delayed by enclosing the perishable product in a chamber to which is applied well recognised methods, such as reduction of temperature below ambient room temperature, and/or the reduction of the concentration of oxygen below that occurring in air, and/or the elevation of the concentration of carbon dioxide above the concentration occurring naturally in air. Each of these conditions may be applied alone or in combination with any or all of the others.
However if the oxygen concentration is reduced too much or the carbon dioxide concentration rises too high, then the perishable product may be injured, resulting in even more rapid deterioration than might occur if no treatment was applied. Consequently it is desirable to be able to adjust the composition of the atmosphere within the chamber and apparatus for adjusting the atmosphere in the chamber has accordingly been developed.
For transportation of perishable produce, the chamber referred to may be a shipping container, which in a common form may be fitted with a refrigeration system to adjust the temperature.
Controlled atmosphere containers are usually purpose built. However, controlled atmosphere apparatus may also be installed in a refrigerated container following a time-consuming and expensive operation.
Controlled atmosphere containers must be substantially sealed in order to separate the controlled atmosphere from the ambient atmosphere. It has been found that the door seals in controlled atmosphere containers are generally the source of most leakage. Every time the door is opened the seal is broken.
In one existing apparatus for controlling the atmosphere in a container, the atmosphere is taken from the container and passed through a device for actively modifying the atmosphere such as a carbon dioxide absorption tower and the modified atmosphere reintroduced into the container. The various devices for actively modifying the container atmosphere are expensive and generally difficult to service during transportation.
Where such apparatus is to be used to convert a refrigerated container to a controlled atmosphere container, holes may need to be made in the container walls to allow the container atmosphere to be drawn from the container to be modified and returned to the container. Such a process may need a permanent modification to be made to a refrigerated container and would be time consuming and expensive.